Polyimides are known in the art for use in the manufacture of integrated circuits including chips (e.g. chip back end of the line), thin film packages and printed circuit boards. Polyimides are useful in forming dielectric interlayers, passivation layers, alpha particle barriers and stress buffers. Polyimides are particularly useful as an interlayer dielectric material to insulate the conductor wiring interconnecting the chips on a multichip module. This is known as thin-filmwiring. A multichip module is an intermediate level of packaging between the chips and the circuit board. Multichip modules are generally known in the art. Multichip modules are made up of multiple layers of power, signal and ground planes which deliver power to the chips and distribute the input/output signals between chips on the module or to/from the circuit board.
A particularly useful class of polyimides for electronic components is made by reacting phenylenediamine (PDA) with an aromatic dianhydride to form a polyamic acid. The polyamic acid is then thermally imidized at an elevated temperature to form the polyimide. Due to the oxidative reactivity of PDA which consequently results in a short shelf life, the PDA is preferably distilled directly into the reaction mixture immediately prior to the polymerization reaction. The use of the dihydrochloride salt of PDA, which is stable in air, is avoided because of the problem of corrosion with residue chloride contamination in the polyimide product. There is no commercially practical procedure for removing chloride from the resulting polyamic acid. There is still a need in the art for an improved process for making polyimides comprising PDA which does not require a cumbersome distillation of the starting material.
It is therefore an object of the present invention to provide an improved process for making polyimides.
Other objects and advantages will become apparent from the following disclosure.